Abstract: For firm installation at a water bottom, a mooring anchor for securing a basal end of a mooring line underwater includes an anchor assembly to which the mooring line is to be fastened, and installable at a water bottom, and a guide to be secured at the water bottom at a position away from the anchor assembly and including a holder to receive and hold the mooring line in a movable manner. The anchor assembly includes a pile drivable into the water bottom and a tilted support extending obliquely downward toward the guide at the water bottom and to be embedded in the water bottom, such that the tilted support withstands and overcomes a tensile force acting in a horizontal direction.